In accordance with depletion of fossil fuels and environmental impact problems, many researchers actively concentrate on development of alternative energy. Secondary batteries are also intensively researched in a variety of fields as an alternative energy. The battery field expands to conventional portable devices as well as batteries for automobiles and batteries for power storage.
Representative components constituting the battery include a cathode, an anode, an electrolyte, a separator and the like. Of these, the components having the greatest effects are the cathode and the anode in which an electrochemical reaction substantially occurs.
In particular, a lithium secondary battery uses lithium (Li), as can be seen from the name, and has high energy density and is light in weight, but is disadvantageously dangerous in that it readily produces dendrites. Specifically, during charging, electricity is stored through transfer of Li ions from the cathode to the anode. In this process, at an initial charging stage, Li ions are supplied from the cathode through an electrolyte to the anode and polarization occurs at the interface between respective materials, thus causing overcharge. At this time, movable ions are insufficient as compared to flowing current and Li is thus precipitated due to overvoltage. The lithium precipitation is caused by movement of lithium ions as well as electric resistance and movement of ions is closely related to porosity of electrodes or the like. As porosity increases, mobility of Li ions increases, but electric contact decreases. Accordingly, balance between porosity and mobility of Li ions is required, but is considerably difficult. In particular, disadvantageously, high porosity inevitably entails low energy density. In this regard, a first attempt to commercialize a secondary battery using a Li-metal as an anode was failed due to safety problems.
At present, a graphite-based material enabling charge/discharge of Li is generally used for an anode. However, this graphite-based anode active material has a considerably small difference between charge and discharge voltages as compared to lithium, thus having a problem in that Li dendrites are readily produced by electrochemical reaction or overvoltage or polarization occurring in devices.
Also, a great amount of byproducts generated by side reactions are accumulated near generated dendrites and deterioration in cycle functions and in serious cases, byproducts pass through the separator, thus causing micro short-circuit and explosion or the like.
Accordingly, many researches attempt to devise methods for preventing formation of Li dendrites, but cannot yet obtain results satisfying current circumstances requiring higher energy density.